Refrigerating system with means to obtain high liquid line pressure



April 5, 1960 J. E. WATKINS 2,931,191

REFRIGERATING SYSTEM WITH MEANS TO OBTAIN HIGH LIQUID LINE PRESSUREFiled March 9, 1956 2 Sheets-Sheet 1 was Wu: 5

"Elsi/IE sumo/rs Man! For conpnssvxh April 5, 1960 J. E. WATKINSREFRIGERATING SYSTEM WITH MEANS TO OBTAIN HIGH LIQUID LINE PRESSURE 2Sheets-Sheet 2 Filed March 9, 1956 J 115 J J J95 J J65 J J 19: us :15

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JAN EB MAR APR HIV JUI'E JULY N6 SEP OCT NO 0! MONTH United StatesPatent D REFRIGERATING SYSTEM WITH MEANS TO OBTAIN HIGH LIQUID LINEPRESSURE John E. Watkins, Maywood, Ill. Application March 9, 1956,Serial No. 570,620 14 Claims. (Cl. 62-174) This invention relates to arefrigerating system, and more particularly a commercial or industrialrefrigerating system of the large capacity type having a plantcompressor, a condenser into which the compressor discharges which maybe either an evaporative condenser or a conventional shell-and-tubecondenser, a receiver for .storing the refrigerant liquefied in thecondenser, and a plurality of plant evaporator coils connected toreceive liquid refrigerant from the receiver under high liquid linepressures.

In such refrigerating systems, the liquid line pressure is imposeddirectly by the plant compressor with its values set by the condenserscapacity. Furthermore, the minimum pressure differential between thehigh and low sides of the system is predetermined and fixed by thethermal expansion valves and flow valves at the evaporator cooling coilswhich require considerable pressure drops through their orifices inorder to deliver rated capacity. It is the general practice in plantscontrolled by such instrumentalities, to maintain high liquid linepressures and corresponding high diflerential pressures between the highand low sides of the system, by maintaining high compressor dischargeand high condenser pressures, and to operate the system year around atsuch high liquid line pressures. With evaporative type condensers whereoutside air is circulated through the condenser coils, condenserpressures vary in accordance with well known thermo-dynamic principlesas determined by the wet bulb temperature of the outside air, generallyfollowing seasonal fluctuations in temperature and producing highercondenser pressures during the warmer months and lower condenserpressures during the colder months of the year. During the colder monthsof the year when condenser pressures would ordinarily fall, the high andrequired condenser pressures are maintained by stopping fans, shuttingofi spray pumps and/or restricting spray water supply, thus raising thetemperature of the cooling fluid.

It will readily be apparent that refrigerating systems operated in thismanner are extremely ineflicient. The same may be said for systemsemploying shell-and-tube type condensers utilizing water circulatedthrough the condenser rather than air for the cooling medium. In suchsystems, notwithstanding the fact that water temperatures varysubstantially between the warmer and the colder months, the generalpractice again is to increase condenser pressures during periods whenthe water supplied to the condenser is at colder temperatures, tomaintain higher liquid line pressures than would otherwise be producedin the condenser. by restricting the water supply or by shutting offcertain of the banks of the condenser surface during the periodsmentioned effectively producing higher condenser pressures.

Greater efiiciency has been obtained by setting the controlinstrumentalities at the evaporator cooling coils for overfeeding atminimum condenser pressures as are experienced during the colder months,and by having the excess of liquid refrigerant produced in the systemduring This may be accomplished.

the warmer months and which would normally flood the evaporator coilsrecirculated through the evaporator coils for cooling purposes. Such asystem is disclosed in my Patent No. 2,590,741, issued March 25, 1952.

It is a general object of this invention to provide as did therefrigerating system disclosed in the aforesaid patent, for evaporativecooling with a minimum pressure differential between the high and lowsides of the system and maintaining liquid line pressure constantthroughout the year regardless of the condensing pressure, but in thepresent instance by obtaining high liquid line pressure by meansseparate, apart and distinct from, yet working in conjunction with, theplant compressor.

It is a further object to provide a refrigerating system where condenserpressures are maintained at the lowest possible value as determined bythe temperature of the cooling fluid circulating through the condenser,while liquid line pressures are maintained at a relatively high presetvalue and steady at that value for year round operation regardless ofthe condensing pressure.

It is a more specific object of this invention to provide arefrigerating system in which condenser pressures are maintained atminimum value as determined by the temperature of the cooling fluidcirculated through the condenser, where liquid refrigerant is taken fromthe receiver at condenser pressure and compressed by pressure imposingmeans other than the plant compressor to a preset pressure as requiredby the operating characteristics of the system, and where the liquidrefrigerant is then forced at this preset pressure through the liquidline to the evaporator cooling coils.

it is another object of this invention to provide a refrigerating systemin which a pressurizing system is incorporated, operative when condensertemperatures and pressures fall, for supplying higher liquid linepressures than will normally be produced by the compressor and condenserwhen operating at maximum eificiency. Accordingly, it is an object toprovide a refrigerating system obtaining maximum efiiciency inoperation, one that follows the weather and allows condenser pressuresto rise and fall in accordance with the temperature of the cooling fluidcirculated through the condenser, while maintaining a preset normallyhigher pressure on the entire plant or in the liquid line to theevaporator cooling coils.

Other objects and advantages will become apparent from the followingdescription, taken together with the accompanying drawings wherein:

Figure l is a diagrammatic view of a refrigerating system embodying thepresent invention;

Fig. 2 is a chart illustrating the relation between condenser pressureand brake horsepower for a given compressor;

Fig. 3 is a chart illustrating average annual wet bulb temperatures fora given latitude;

Fig. 4 is a diagrammatic view of a portion of the refrigerating systemof Fig. 1 modified to include a flash tank for removing flash gas fromthe system; and

Fig. 5 is a diagrammatic illustration of a control circuit for certainof the control instrumentalities embodied in the system shown in Fig. 1.

While the invention is susceptible of various modifications, there isshown in the drawings and will herein be described in detail oneillustrative form thereof. It is to be understood, however, that it isnot thereby intended to limit the invention to the specific form dis--in which a liquid refrigerant is supplied from a source to a pluralityof evaporator cooling coils 10. The cool: ing coils, of which there maybe more than the number illustrated, ordinarily would be located indifferent rooms or in different cooling units of the plant, inaccordance with conventional practice as embodied in the construction oflarge capacity commercial type systems.

The source of liquid refrigerant may be of any conventional type and asherein depicted comprises a compressor 11, and a condenser 12 into whichthe compressor discharges. A receiver 13 for storing the liquid refrig'erant produced in the condenser is provided in this system as inconventional systems, andordinarily is located in general proximity tothe plant compressor 11 and the condenser 12 and is arranged to bedrained into a liquid line 14 connected and extending to the remotelocation where the evaporator cooling coils are found. The suction sideof the compressor is connected to a suction line 15 forming the returnline from the low pressure side of each of the evaporator cooling coilsand thus connecting the plant compressor 11 directly with the evaporatorcooling coils.

In carrying out the present invention, to increase op erating efiiciencyof the refrigerating system by allowing condenser pressures to rise andfall in accord with the temperature of the cooling medium circulatedthrough the condenser, in other words, to follow the weather, liquidline pressures are raised to a preset value which is maintainedirrespective of the condenser pressure. In the present instanceprovision is made in the system for raising the pressure of liquidrefrigerant in the liquid line 14. Furthermore, in keeping with theinvention, since the line pressure need only be raised when condenserpressures fall below the preset value, control instrumentalities areincorporated for raising the pressure of the liquid refrigeranteffective upon the condenser pressure dropping below the preset value.Accordingly, in the system shown in Figure 1 of the drawings, apressurizing compressor 16 is included as a part of a pressurizingsystem for raising liquid line pressures. This is accomplished by takingsaturated refrigerant gas from the receiver 13, raising the pressure ofthe refrigerant gas to a preset value, and applying the refrigerant gasunder the preset pressure by means of a gas line 17 to liquidrefrigerant contained in a pair of displacement tanks 18, 19, whichserve as reservoirs, and for this purpose are connected by a supply line14 to the receiver for receiving liquid refrigerant. Thus thepressurizing system is used for raising the pressure of the liquidrefrigerant in the liquid line to the preset value and for forcing theliquid refrigerant through the liquid line to the evaporator coolingcoils.

Referring specifically to Figure 1 again, the liquid line 14 extendingto the plurality of evaporator coils, is divided into two branches 14',14" between the receiver 13 and the coils for connection to the pair ofdisplacement tanks 18, 19. These displacement tanks may comprisecylindrical sheet metal tanks of conventional construction, having meansshown in the present instance'as displacement switches 21, 22 forregulating theadmission of liquid refrigerant into the respectivedisplace ment tanks from the receiver 13.

These displacement switches, which may be Magnetrol liquid levelcontrols, or may be simple float switches, are used not only forregulating the admission of liquid refrigerant to the tanks, but arealso used to regulate the admission to these tanks of refrigerant gasunder pressure from the pressurizing compressor 16 for forcing theaccumulated liquid into the liquid line to the evaporator cooling coils.7

Accordingly, both displacement tanks 13, 13 are connected by a shortsegment of supply line 23, 24 to the respective branches '14, 14 of theliquid line 14. Furthermore, on both sides of the junction between thesupply lines 23, 2d and the respective branches of the liquid line,check valves 25, 26 and 27, 28 are incorporated in order to allow flowfrom the tanks 18, 19 into the liquid line 14 to the cooling coils whilepreventing reverse fiow toward the receiver 13.

For venting the displacement tanks to the suction line 15, in theconstruction and arrangement illustrated, vent conduits 29, 30 areemployed, meeting and connected by means of a common vent line 31directly to the suction line 15 extending to the plant compressor. Inthe vent conduits 29, 39 extending respectively to the displacementtanks 18, 19, vent valves 32, 33 are interposed for controlling theventing of the respective displacement tanks.

The displacement tanks 18, 19 are connected to the gas line 17 by meansof these same vent conduits 29, 30 and also branches 34, 35 of the gasline 17. In the branches 34, 35 of the gas line 17, gas valves 36, 37are interposed for controlling the admission of high pressure gas to thedisplacement tanks.

The. arrangement and construction illustrated enables the supplying ofeach of the displacement tanks alternately with liquid refrigerant fromthe receiver and for alternately admitting refrigerant gas under thepreset pressure from the gas source. The displacement type or float typeswitches 21, 22 are accordingly arranged for controlling the vent-valves32, 33 and the gas valves 36, 37, for alternately opening the respectivedisplacement tanks 13, 19 to the source of refrigerant gas under thepreset pressure or to the suction line to vent the displacement tanks.With the check valves interposed between the respective displacementtanks and the receiver 14, liquid from the receiver is introduced intoeach of the displacement tanks alternately while gas is being vented,until high liquid levels are reached when the gas valves 36, 37 areopened, admitting gas under the preset pressure to force the accumulatedliquid into the respective branches of the liquid line through the checkvalves, which permit drainage from the receiver while preventing reverseflow from the displacement tanks.

While the multiple vent and gas valves may be operated manually, it iscontemplated that the use of automatic controls will be desired forautomatically raising the pressure of liquid taken from the receiver tothe preset value as required by the plant, and forcing the liquidrefrigerant through the liquid line to the evaporator cooling coils. Forthis purpose, the vent valve 32, 33 and the gas valves 36, 37 aresolenoid operated. As will be seen by reference to the circuit diagramin Fig. 5, solenoids 32', 33 and 36', 37 0f the vent and gas valvesrespectively, are connected in circuit with the float switches 21, 22which automatically control the operation of these valves. The controlcircuit is constructed so that when high liquid levels are reached inthe respective displacement tanks, the gas valves 36, 37 by means of thesolenoid actuators 36' and 37' are opened to admit gas under the presetpressure from the gas line 17. During the period when the gas valves 36and 37 are open, the vent valves 32, 33 are closed to prevent the escapeof gas under pressure from the displacement tanks 18, 19 respectively.Alternately, when low liquid levels are reached in either of the twodisplacement tanks 18, 19 the gas valves 36, 37 are closed to preventthe admission of refrigerant gas under pressure to the displacementtanks, and the respective vent valves 32, 33 are opened to vent thetanks to the suction line. Liquid refrigerant is automatically fed intothe displacement tanks due to the differential in pressure between theliquid refrigerant stored in the receiver at condenser pressure and therespective displacement tanks.

In order to reduce re-expansion losses a pressure regulator valve 40 isinterposed in the vent line 31 between the displacement tanks and thesuction line. The function of this valve 4% is to control the venting ofthe displacement tanks, and thus the pressure therein prior to fillingwith liquid refrigerant from the receiver 13.

With a manually operated type valve, the valve 40 is set to allow therespective displacement tanks to vent until a predetermined low pressureis obtained. With an automatically operated valve, the valve 40 may beconnected as by a control line 55, to the receiver so as to control thepressure in the displacement tanks to maintain the pressure therein afew pounds below the receiver pressure. The operation of such anautomatic valve will be explained in detail below. With a manuallyoperated valve 40 in the system, the setting is determined as follows.This pressure regulator valve 40 is set to allow the respectivedisplacement tanks to vent until a predetermined low pressure isobtained. For a particular system and refrigerant, the minimum condenser(and receiver) pressure that is experienced even in the coldest monthsof the year may readily be determined. The pressure regulator valve 40should be set to allow the displacement tanks to vent to a pressureslightly less than this minimum condenser pressure. Accordingly thepressure regulator valve operates to close the vent line 31 upon theattainment of the low and predetermined pressure in the displacementtanks.

In the gas line 17 between the displacement tanks 18, 19 and thepressurizing compressor 16, in the present instance there is interposeda gas receiver 45 for receiving and storing refrigerant gas under thepreset pressure as supplied from the pressurizing compressor. Formaintaining the preset pressure in the gas receiver 45, a pressureswitch 47 may be used, a switch of any conventional construction,arranged to control the operation of the pressurizing compressor, andfor that purpose connected in circuit with the compressor motor (notshown), in order to maintain at a steady and uniform value and at thedesired preset level the pressure of refrigerant gas in the gas receiver45. A check valve 46 vent reverse fiow from the gas receiver 45. The gasreceiver 45 is employed primarily for maintaining a minimum of surgingand short cycling by providing means for storing the compressed gastemporarily on its intermittent or periodic application to thedisplacement tanks 18, 19.

Also for controlling the operation of the pressurizer compressor 16, apressure switch 50 may be incorporated in the discharge line 51 from theplant compressor 11. In the present instance, a pressure switch 50 ofconventional construction is used, electrically connected to the motor(not shown) driving the pressurizing compressor 16 and set to start thepressurizing compressor when the condenser pressure (or plantcompressor), falls below the required liquid line pressure. A line 52 isused to supply gas under pressure from the plant compressor to the gasreceiver 45. Gas is allowed to pass through the line 52 when thedifferential between the discharge pressure of the plant compressor andthe pressure in the gas receiver exceeds a value as determined by therelief valve 53 which also acts as a check valve to prevent reverse flowof gas.

In the particular system illustrated in Figure 1 of the drawings, theplant compressor operates continuously for maintaining suction pressurein the suction line from the plant, and continuously circulatesrefrigerant gas from the evaporator cooling coils through the compressorwhere the gas is compressed and discharged into the condenser where itis liquefied for cooling purposes in the plant.

Referring to Figs. 2 and 3, charts which will be used for illustratingthe operation of a refrigerating system including the pressurizingsystem as hereinbefore described, it will be observed that Fig. 3includes two similar curves, one of which is curve A using thehorizontal coordinant and the left-hand vertical coordinant andillustrating the average wet bulb temperature during the year in theChicago latitude. Curve B indicates the relationship of averagecondensing pressures at constant capacity with evaporative condensing,using the right is used to predischarge pressure from the 6 handvertical coordinant of the chart. The average over all wet bulbtemperature during the year is indicated by the dashed horizontal line Cwhile the average noon wet bulb temperature, slightly higher than theaverage over-- all wet bulb temperature, is indicated by the horizontaldash-dot line D. p

The average overall condenser pressure is indicated by the dotted lineB, and is computed from the average condensing pressure curve B whichgives values for noon average wet bulb temperatures and thus must bemodified, in the present instance by deducting five pounds, in order toobtain the overall average.

With the system illustrated in Figure 1 of the drawings, condenserpressures are allowed to rise and fall in accordance with wet bulbtemperatures, limited only by the necessity for shutting off spray waterin the event the temperature falls below freezing. The-average condenserpressure encountered during the year would be as given in the chartshown in Fig. 3, established at a value of 105 pounds per square inchgauge. Values of pressure hereinafter set forth will be given in termsof p.s.i., designating in all cases gauge pressure.

Turning to the chart shown in Fig. 2, this depicts a' family of curvesfor different suction pressures maintained by a plant compressor ofconventional construction, and relates brake horsepower per ton ofrefrigeration (in this case ammonia) with the condensing pressures. Thespecific values in this chart were obtained from an 8" x 8" two cylinderV.S.A. compressor operating at 400 rpm.

In a refrigerating system using ammonia for the refrigerant, 25 p.s.i.suction pressure might be representative of conventional systems. Withan average condenser pressure of 105 p.s.i. as obtained from the chartshown in Fig. 3, the brake horsepower per ton of refrigeration isillustrated by the chart of Fig. 3 to be approximately .92.

To compare, conventional refrigerating systems without the pressurizingsystem component as illustrated in Figure l of the drawings, operatingat 25 p.s.i. suction pressure may require a condensing pressure as highas 165 p.s.i. the year around, in order to provide sulficient liquidline pressure for the plant. From the chart shown in Fig. 2, such aconventional refrigerating system operating with an average 165 p.s.i.condenser pressure requires l.3l brake horsepower per ton ofrefrigeration.

From the foregoing it will be seen that by embodying in a refrigeratingsystem means for raising and maintaining the liquid line pressure at apreset value regardless of the condenser pressure, substantial economiesare effected in the power required to operate the plant compressor. Theimprovement in efiiciency over a conventional system with a like ratedcapacity may be computed at a reduction of 29.8% in required brakehorsepower per ton of refrigeration.

This reduction in brake horsepower (B.H.P.) per ton of refrigeration isdirectly reflected in savings in power costs required to operate theplant compressor.

The pressurizing compressor motor for example, taking a IOU-ton plantusing ammonia, may be of the order of a two horsepower unit. Duringperiods of low condenser pressure (refer to Fig. 2), for example atsuction pressure of 25 p.s.i. and condenser pressure of p.s.i., thetotal load is 71 B.H.P. With 165 p.s.i. condenser pressure the load is141 B.H.P., a difference during such periods of 60 B.H.P. The twohorsepower pressurizing compressor motor during these periods, in thepres surizing system of this invention elfects a savings of 60 B.H.P.for such a plant.

Taking the l00-ton ammonia plant, for purposes of illustration, it maybe assumed that in such a plant 40 pounds of liquid ammonia per minuteare circulated through the system. Assuming also that the system is tobe operated with a liquid line pressure of 165 p.s.i. and an averagecondenser pressure of p.s.i. it is thus necessary to raise the pressureof the liquid arn monia an average of 60 p.s.i. The size of compressormotor required to raise 4 0 pounds of liquid ammonia perv minute anaverage of 6 p.s.i. may be computed as follows:

4.0 (poundslXBO .s.txae .26 HP 33,0GOXEti. *aa.

Taking into account peak load which may be twice the average load, fromthe above computation it will'be seen that a 2 horsepower motor atordinary efliciency supplies suflicient power to drive the pressurizingcompres sor at a rate suflicient to increase the liquid ammonia pressurethe required average 66 pounds per square inchtion with the pressureregulating valve 40 included inv the vent line 31 between thedisplacement tanks and the suction line, for maintaining a minimumpressure in the displacement tanks which varies as the receiverpressure. In the system illustrated in Fig. l of the drawings, and asdescribed hereinbefore, the pressure regulator valve 40 may be set toallow the displacement tanks to vent to the suction line to reduce thepressure in the tanks to a preset value, the preset value beingdetermined by the minimum receiver pressure which would be experiencedduring the colder months of operation.

Referring to Fig. 1, it will be seen that provision may be made as shownby the control line 55 forconnecting the pressure regulator valve 40 tothe receiver 13, for controlling the pressure regulator valve operationin accordance with the receiver pressure. In this instance the pressureregulator valve 40 may be of conventional construction, embodying adiaphragm connected to the working parts of the valve above which thecontrol line 55 connection to the receiver is made. This maybe termed ableeder connection". Pressure regulator valves of the foregoing type,termed in the art as modulating back pressure valves, and having aspringworking to operate against the diaphragm and against the backpressure are of ordinary conventional construction and are readilyavailable. With such an arrangement; embodied in the system of Figure l,the pressure regulator valve '40 is set to maintain a minimum pressurein the displacement tanks 18, 19 which varies as the receiver pressure,and amounting to a predetermined few pounds below the receiver pressure.

During periods of the year when high condenser pressures and thusreceiver pressures are experienced, it is unnecessary to have theminimum pressurein the displacement tanks reduced by venting to the samevalues which would allow the system to operate when low condenser andreceiver pressures are experienced, as for example are encountered inthe colder months of the year. By including a pressure regulator valvewhich controls the displacement tank pressure in relation to thereceiver pressure, considerable re-expansion losses are eliminated.

In a further aspect of the invention it is contemplated that means maybe included for reducing the pressure of the liquid refrigerant obtainedfrom the source in order to remove a portion of the flash gas from theliquid refrigerant prior to repressurizing and feeding to the plantevaporator coils. The pressure reduction to be effected by this meansneed only be suflicient to remove that quantity of flash gas which wouldotherwise be produced as an incident to the pressure drop of the liquid;refrigerant flowing through the lines from the repressurizing system tothe evaporator cooling coils.

In the present instance, as shown in Fig. 4 (where k r fer n e, n me asw he r. n lud d n. gu 1.-

are used to designate like components), a flashtanlg 56 may be locatedin proximity to the receiver 13 and in the liquid line 14 between thereceiver and the displacement tanks 18, 19. Pressure reduction iseffected in the present instance by a pressure reducing valve 57 ofconventional construction interposed in the line 14 and adapted to beconnected by means of a compensating line 57 to the suction line 15. Asimple expansion valve could also be used in place of the pressurereducing valve, as preferred Associated with the flask tank 56 is alevel responsive control valve 56' which may be of any suitable typeadapted to maintain a constant liquid lever in the tank. When the levelfalls the valve opens to vent the flash gas from the tank through aconduit to the suction line 15. Pressure in the tank is thus reducedcausing the pressure regulating valve 57 to admit more liquidrefrigerant to the tank.

As shown in Figure l, with the flash tank or flash chamber 56 included,by means of the pressure reducing valve 57, liquid refrigerant drainedfrom the receiver 13 may be flashed down to a pressure considerablyabove suction pressure, but suflicient to remove flash gas which wouldnormally be produced in the lines, fed to the displacement tanks 18, 19and repressurized in order to obtain a supply of subcooled liquid forfeeding to the evaporator cooling coils. The temperature of the liquidrefrigerant in the flash tank 56 is below the temperature or the liquidin the receiver 13 as determined by the.

condenser 12, and considerably below the saturated tempertaure at thepressure of the refrigerant gas in the displacement tanks. Thus afterthe liquid has been repressurized it is in the subcooled state. The heatgiven off during the operation of pressure reduction to produce this lowtempertaure of the liquid refrigerant is absorbed in the transformationof a portion of the liquid refrigerant into flash gas.

The advantages to be gained by including the pressure reducing means asjust before described, may be more graphically explainedby comparing theoperation of the system as illustrated in Fig. 4, with a conventionalsystem including a flash tank, and with a system like that disclosed inFig. l of the aforementioned Patent No. 2,590,741, issued March 25,1952.

With the present system, the pressure regulator valve 57 may be set toreduce the pressure of the liquid refrigerant to a predeterminedpressure, some substantial value above the maximum suction pressureexperienced in the normal operation of the system. By means of thepressurizing compressor 16 and the displacement tanks 18, 19 andassociated controls, the liquid refrigerant atthis low pressure, and atthe corresponding low temperature is then subjected to the presetpressure of substantially p.s.i. and fed to the cooling coils. No flashgas is produced in the liquid lines extending to the expansion valvesand evaporation cooling coils, and a solid supply of liquid refrigerantis produced for cooling purposes.

In a conventional system including a flash chamber and having expansionvalves at the evaporator cooling coils sized for substantial pressuredrops, liquid refrigerant taken from the receiver at condenser pressureis reduced in pressure for removing a portion of the flash gas from theliquid. In such a system the liquid is fed at flash tank pressure to theevaporator cooling coils. Flash gas, therefore, is produced in the lineas an incident to the pressure drop therein. This flash gasdeleteriously affects the eficiency of operation of the various valvesin the system.

In a system like that shown in the aforementioned Watkins Patent No.2,590,741, issued March 25, 1952 the flash tank pressure is employed forfeeding the liquid refrigerant to the evaporator cooling coils. Thusflash gas is produced in these lines affecting unfavorably the operationof the system. With a pressurizing system, as

described hereinbefore, to provide subcooled. liquid for erant into theliquid line for feeding to the cooling coils.

As'desc'ribed hereinbefore,'provision is made for auto-- purposes ofcompleteness of description, an exemplary.

control circuit is shown in Fig. 5, illustrating the electricalconnections between the float or displacement switches 21, 22, the ventvalves 32, 33 and the gas valves 36, 37 included in the pressurizingsystem. In this exernplary, control circuit, initial closure of switch21 conrolling the admission of liquid refrigerant and the admission ofrefrigerant gas under the preset pressure to displacement tank 18,operates upon low liquid levels being. reached in the tank to close thegas valve 36 by opening contacts 59 and de-energizing the solenoid 36'of the. gas valve. Simultaneously contacts 58 are closed, energizing thesolenoid 32 of the vent valve 32. The displacement tank 18 isaccordingly vented to the suction 1i'ne 15 through vent line 31, andautomatically the pressure therein is reduced either to preset minimumpressure by the pressure regulator valve 40, or to a pressure a fewpounds per square inch less than the pressure in receiver 13. By reasonof the differential in pressure between the receiver 13 and the tank 18,liquid refrigerant is drained from the receiver and introduced in thebottom of the said tank. Upon the liquid level in the tank reaching thehigh level, the float switch 21 operates tgwreverse the arrangement,closing the vent va ve 32 by die-energizing the solenoid 32' thereof,and opening the gas 'line valve 36 by making the circuit to the solenoid3,6 ofthe valve, and thus allowing refrigerant gas under thepresetpressure to be admitted into the displacement tank 18 to apply thepreset pressure to the accumulated liquid therein and to force theliquid into the branch 14' Qfthe liquid line and thence into the liquidline 14 itself. Reverse flow of the liquid is prevented by check valve26 connected in the branch 14' of the liquid line and betl weenfthedisplacement tank 18 and the receiver 13.

'15 The float switch 22 controlling the admission of liquid rjefrigerantand refrigerant gas under preset pressure to displacement tank 19,operates in a similar manner. l'hu's when the low liquid level isreached, the switch 22 by. means of contacts 60 closes the circuit tothe vent vla'lve solenoid 33, opening the vent valve and venting thetank, the solenoid 37 of the corresponding gas valve during this periodbeing de-energized and the valve being closed. When the'tank is filled,the arrangement is reversed, the solenoid 37 energized and the gas valveopened to admit high pressure gas to the tank, and the solenoid 33de-energized and the vent valve 33 closed.

if It will also be noted that the circuit to the switch 22 controllingthe displacement tank 19 is arranged across the contacts 58. 59 operatedby the float or displacement valve 21 in the other tank 18. Thearrangement is such that the contacts 59 must be closed to energize thesolen'oid 33, and open the corresponding vent valve. These eontacts areclosed only when the liquid in the tank 18 at a high level and theswitch 21 is in its raised position. Similarly, to energize the solenoid37 and open the gas valve 37, the contacts 58 must be closed, thesecontacts being closed only when the tank 18 is empty.

.With the control illustrated as exemplary, the displacement tank 18controlled by the displacement or float switchv 21 provides the primarysource of liquid refrigerant'v under pressure for the liquid line, thetank 19 being employed to supply liquid refrigerant under the requiredpressure onlyduring refill of the tank 18. The control circuitillustrated in Fig. also shows an exemplary arrangement for the pressureswitches 47 and stipplying to the evaporator cooling coils, thisflashgas may be removed prior to introducing the liquid refrigis i 5i)controlling the operation of the motor driving the gizing the relay 62to close the motor circuit and thus start the motor.

I claim as my invention:

1. A refrigerating system, comprising, a compressor,

a condenser into which said compressor discharges for producing liquidrefrigerant and arranged to receive cool- 1 ing fluid the temperature ofwhich varies circulated through it, a cooling coil, and a liquidrefrigerant circulating circuit connecting said coil to the condenserand compressor including a liquid line for conveying the refrigerant tothe coil from the condenser, the feeding of liquid refrigerant throughthe system requiring a. liquid line pressure determined by the pressuredrop through the system, which pressure is normally supplied by thepressure in the condenser, and a pressurizing systern connected in saidliquid line, said pressurizing system including means connected to theline for receiving liquid refrigerant at the line pressure, and meansassociated with said receiving means for applying pressure to the liquidrefrigerant to raise its pressure, and control means for operating saidpressurizing system when condenser temperatures and pressures fall forraising the pressure of liquid refrigerant in the line above thepressure in the condenser to the pressure required to feed the liquidrefrigerant through the system so as to obtain maximum operatingefliciency by allowing condenser pressures to rise and fall inaccordance with the temperature of the cooling fluid circulated throughthe condenser.

2. In a refrigerating system, the combination compris ing, a receiverfor storing liquid refrigerant under pressure, the pressure in saidreceiver varying over a substantial range, a cooling coil, a liquid linefor conveying liquid refrigerant to said cooling coil from saidreceiver, the feeding of liquid refrigerant through the system requiringa liquid line pressure determined by the pressure drop through thesystem, the system being arranged so that the receiver pressure isnormally above said required pressure, and means in said liquid line forraising the pressure of the liquid therein to the pressure required tofeed the liquid refrigerant through the system when the receiverpressure drops below said required pressure, said last-named meansincluding a reservoir connected to the line for receiving liquid, andpressure applying means associated with said reservoir for raising thepressure of the liquid refrigerant therein sufliciently to overcome saidpressure drop to pump the refrigerant from the reservoir through theliquid line to the cooling coil.

3. A refrigerating system having, in combination, a compressor, acondenser into which said compressor discharges, a receiver for storingthe refrigerant liquefied in said condenser, an evaporator cooling coil,a refrigerant circulating circuit including a liquid line for conveyingliquid refrigerant from said receiver, a pressurizing system connectedin said liquid line'for feeding liquid re frigerant from the receiver tothe cooling coil, the feeding of liquid refrigerant requiring a pressurein the liquidline which pressure is dependent upon the pressure dropthrough the system, and a return line connecting the cooling coil to thecompressor, saidpressurizing system including a reservoir for liquidrefrigerant having a connection to the line, pressure reducing means insaid lastnamed connection reducing the pressure of the liquidrefrigerant to a pressure below the pressure required to feed theliquid, a source of gas under pressure, anda con nection between saidsource and said reservoir-"for sup 1i plying gas under pressure to theliquid in the reservoir and raising the pressure of the said liquidtothe required pressure.

4. A refrigerating system having, in combination, a compressor, acondenser into which said compressor discharges and arranged to havecooling fluid the temperature of which varies circulated about thecondenser coils, a receiver for storing the refrigerant liquefied insaid condenser, and a liquid refrigerant circulating circuit connectedto said condenser including a liquid line receiving liquid from saidreceiver, a return line connected to said compressor, and a cooling coilconnected across said lines, the feeding of liquid refrigerant throughthe circuit requiring a liquid line pressure dependent upon the pressuredrop through the circuit, and means connected in the liquid line forpressurizing the liquid in said liquid line when the same drops belowsaid pressure, said pressurizing means including a pair of tanksconnected alternately to the receiver for filling with liquidrefrigerant. and the line for supplying said liquid refrigerant to thecooling coil, and means connected to the receiver for alternatelyapplying pressure to the liquid refrigerant in the tanks.

5. In a refrigerating system, a source of liquid refrigerant underpressure including a receiver, a pair of tanks connected to saidreceiver by conduit means so as to be alternately filled with liquidrefrigerant, pressure reducing means between said receiver and saidtanks for flashing down the pressure of liquid refrigerant supplied tothe tanks below said receiver, pressure, a cooling coil, a liquid lineconnecting said coil with said tanks, a source of refrigerant gas underpressure higher than the pressure of the liquid refrigerant in saidtanks, said source including the receiver, and means for connecting saidsource of refrigerant gas to the tanks for raising the pressure of theliquid refrigerant in each of the tanks when the latter are filled tothe pressure of the source, so as to provide pressure for feeding theliquid refrigerant through said liquid line to the cooling coil.

6. in a refrigerating system having a condenser for the liquidrefrigerant, said condenser being arranged to have cooling fluid thetemperature of which varies circulated through it, a reservoir connectedto receive liquid refrigerant from the condenser and providing means forstoring said liquid refrigerant, an evaporator cooling coil, and aliquid line for feeding liquid refrigerant from said reservoir to saidcoil, the feeding of liquid refrigerant requiring a pressure in theliquid line determined by the pressure drop through the system, thecombination comprising, means connected to said reservoir for applyingpressure to the liquid refrigerant therein, and control means responsiveto the pressure in the condenser-for causing said pressure applyingmeans to operate when the pressure drops below the required liquid linepressure, so as to maintain the pressure of said liquid refrigerant insaid reservoir and in the liquid line irrespective of the condenserpressure as determined by the temperature of the cooling fluid.

7. A refrigerating system having, in combination, a compressor, acondenser into which said compressor discharges and arranged to receivecooling fluid the temperatureof which varies circulated about thecondenser coils, a receiver for storing the refrigerant liquefied insaid condenser, a liquid line receiving liquid refrigerant from saidreceiver, a return line connected with said compressor, a cooling coilconnected across said lines, the feeding of liquid refrigerant requiringa given pressure in the liquid line determined by the pressure dropthrough the system, means for applying pressure to the liquid in theliquid line, and control means responsive tothe condenser pressure foroperating said last-named means so as to maintain the liquid linepressure at a value sufficient to overcome said pressure dropirrespective of variations in the condenser pressure, and effective whencooling fluid temperatures and corresponding condenser pressures fall 29W e P d t mfiaed. alu

8. In a refrigerating system having a-source of liquid refrigerant andrefrigerant gas under pressure including a compressor, a condenser, anda receiver connected to said condenser for storing said liquidrefrigerant and refrigerant gas under pressure; an evaporator coolingcoil; and a liquid refrigerant circuit including a liquid lineconnecting said receiver to said coil, the. combination comprising, areservoir connected in said liquid line, pressure reducing means betweensaid receiver and reservoir for flashing down the pressure of liquidrefrigerant supplied to the latter, and means connected to said sourcefor applying compressed refrigerant gas to said reservoir and raisingthe pressure of said liquid refrigerant so as to provide pressure forforcing the liquid refrigerant through said liquid line to the coolingcoil.

9. In a refrigerating system the combination comprising, a compressor, acondenser into which said compressor discharges and arranged to havecooling fluid the temperature of which varies circulated about the comdenser coils, said condenser and compressor constituting a source ofliquid refrigerant under pressure, an evapo rator cooling coil, a liquidline for feeding liquid refrigerant from said source to said coolingcoil, the feeding of liquid refrigerant requiring a given liquid linepressure determined by the pressure drop through the system, a reservoirin said liquid line, pressure reducing means tween said condenser andreservoir for flashing down the pressure of liquid refrigerant suppliedto the latter, and means for raising the pressure of the liquidrefrigerant in the reservoir to a value sufficient to overcome thepressure drop and which is maintained irrespective of the condenserpressure as determined by the temperature of the cooling fluid, so as toprovide pressure for feeding the liquid refrigerant to the cooling coil.

10. In a refrigerating system, the combination comprising, a receiverfor storing liquid refrigerant under pressure, a cooling coil, a liquidline for feeding liquid. refrigerant to said cooling coil fromsaidreceiver, said liquid line having a pair of branch lines therein, apair of displacement tanks, one of said tanks being interposed in ach ofsaid branch lines, a source of refrigerant gas under a preset pressure,gas lines connecting said displacement tanks and said source ofrefrigerant gas, valves said liquid and gas lines for controlling theflow of liquid, and gas respectively, and means for operating saidvalves for filling each of said displacement tanks alternately withliquid refrigerant from the receiver and refrigerant gas from the gassource, and for admitting liquid refrigerant alternately from each ofsaid tanks to the liquid line connected to the cooling coils whereby toforce the liquid refrigerant in said tanks at said preset pressure. intosaid liquid line and to the cooling coils.

11. In a refrigerating system, the combination comprising, a source ofliquid refrigerant under pressure, a pair of reservoirs for storing saidliquid refrigerant, conduits connecting said source and said reservoirs,a cooling coil, a liquid line for feeding liquid refrigerant to saidcoil from said reservoirs, a source of refrigerant gas under presetpressure normally higher than the pressure of the liquid refrigerant insaid reservoirs, a gas line for supplying gas from said source ofrefrigerant gas to said reservoirs for placing the liquid refrigerantstored therein under the preset pressure, valves for regulating thesupplyof liquid refrigerant and refrigerant gas to said reservoirs andfor admitting liquid refrigerant to the, liquid line from saidreservoirs, and means for controlling said. valves for supplying each ofsaid reservoirs alternately with refrigerant gas and liquid refrigerantfrom the respective sources thereof whereby to fill the reservoirs withliquid refrigerant from the source. thereof and to,

raise the pressure of the liquid refrigerant stored in said reservoirsto the pre-set pressure, and for admitting liquid refrigerant at thepre-set pressure to the liquid line. ternately from each of saidreservoirs to feed the cooling coil. i

12. A refrigerating system comprising, in combination, a compressor, acondenser into which said compressor discharges and arranged to receivecooling fluid the temperature of which varies circulated through it, areceiver connected to said condenser for storing the refn'gerantliquefied in said condenser, a pressure reducing valve and flash chamberreceiving liquid refrigerant from the receiver for reducing the pressureof the liquid re frigerant below the receiver pressure and removingflash gas therefrom, the liquid in said flash chamber being sub-cooled,and a liquid refrigerant circuit including a liquid line connected tothe flash chamber, an evaporator cooling coil connected to the liquidline, and a return line connecting the cooling coil to the compressor,the feeding of liquid refrigerant through the circuit requiring a liquidline pressure determined by the pressure drop through the system, andmeans for pressurizing the sub-cooled liquid refrigerant obtained fromthe flash chamber and fed through the liquid line to the cooling coil,to a pressure suflicient to overcome said pressure drop, which latterpressure is maintained irrespective of variations in the condenserpressure, so that condenser pressures are allowed to rise and fall inaccordance with the temperature of the cooling fluid circulated throughthe condenser.

13. In a refrigerating system, the combination comprising, an evaporatorcooling coil, a source of liquid refrigerant under pressure, a pair ofreservoirs for storing said liquid refrigerant, supply conduitsconnecting said source and said reservoirs, a source of refrigerant gasunder pre-set pressure normally higher than the pressure of the liquidrefrigerant obtained from the source thereof, gas supply conduitsconnecting said source of refrigerant gas and said reservoirs, ventlines connected to the reservoirs, a pressure regulator connected tosaid vent lines, said pressure regulator being effective to regulate theventing of said reservoirs to obtain a vented pressure in saidreservoirs a predetermined relatively small amount below the pressure ofthe liquid refrigerant obtained from said source to allow filling thereservoirs with liquid refrigerant from the source thereof, a liquidline connecting said evaporator cooling coil with said reservoirs forfeeding liquid refrigerant obtained alternately from each of saidreservoirs to said cooling coil, valves in said iiquid and gas supplyconduits and vent and liquid lines, and means for controlling the saidvalves for alternately filling the reservoirs with liquid refrigerantplacing the liquid refrigerant therein under the pre-set pressure of thegas and admitting liquid refrigerant at said pre-set pressurealternately from each of said reservoirs into the liquid line forfeeding to the cooling coil.

14. In a refrigerating system, the combination comprising a source ofliquid refrigerant including a compressor and a condenser through whichcooling fluid is circulated the temperature of which varies, thedischarge pressure of the compressor being variable in accordance withthe temperature of the cooling fluid circulated through the condenser, areceiver connected to the condenser, a tank for liquid refrigerantconnected to the receiver, a liquid line receiving liquid refrigerantfrom said tank, the feeding of liquid refrigerant requiring a givenpressure in the liquid line determined by the pressure drop through thesystem, means between the receiver and tank for reducing the pressure ofliquid refrigerant obtained from said receiver and supplied to the tankby flashing down the liquid refrigerant to a sub-cooled state, and meansfor maintaining the sub-cooled liquid refrigerant in said tank at apredetermined pressure suflicient to overcome said pressure dropirrespective of the compressor discharge pressure.

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